Generally, teeth receiving a relatively intensive damage by caries and the like are restored by adhering crown, bridge, inlay, onlay and the like which consist of ceramics, polymer materials, or metal materials by using a resin cement.
Resin cements are required to have a sufficient mechanical strength and a sufficient adhesion strength to dental hard tissues. Otherwise, it is possible that a resin cement comes out during long use in severe oral circumstances and that gaps form at an interface between a resin cement and dental materials and bacteria come in by the gaps to deteriorate dental pulp.
Resin cements may be categorized into a poly(methyl methacrylate) (PMMA) type and a composite type. The PMMA type resin cement comprises PMMA and methyl methacrylate and it has a poor mechanical strength but is excellent in impact resistivity and adhesiveness to a variety of materials. On the other hand, the composite type resin cement comprises dental polymerized monomers and organic composite materials and filler such as glass, silica and the like, and is excellent in adhesion as well as material properties after curing such as a flexural strength, a compressive strength and the like. Therefore, clinic dentists make proper use of two types of resin cements depending on purposes and cases.
Recently, resin cements are highly required to use as adhesive for dental prosthetic materials with esthetics. Resin cements for this purpose should have a high mechanical strength. Therefore, in this field, a composite type resin cement is used because it has an excellent mechanical strength. Such a composite type resin cement usually has a filler content of 50% by weight or higher in order to achieve a high mechanical strength.
As for a conventional composite type resin cement, a powder-liquid type has been mainly used, in which, for example, filler (cement powder) and a monomer solution are provided in a two-package type and the powder and the liquid are mixed just prior to use.
Japanese Patent No. 1784478 [Patent Document 1] discloses in its specification that a dental restoration composition containing radical polymerizable monomers such as methyl methacrylate and the like and curing agents including organic peroxide, amine, a barbituric acid derivative, and acid anhydride or phosphate.
However, such a powder-liquid type resin cement is not clinically satisfactory from a viewpoint of workability in mixing.
Accordingly, a requirement for a two-paste type resin cement is increasing, in which two previously-prepared pastes are mixed in order to avoid complexity in mixing powder and liquid. This two-paste type resin cement is a preferable form for clinicians because mixing two pastes reduces a mixing time and person to person variation comparing to mixing powder and liquid.
Mechanisms for curing a resin cement include chemical polymerization and photo polymerization. When a resin cement is cured only by chemical polymerization, a surface curing degree of the resin cement is low and a non-polymerized layer forms on the surface where the cement exposes because polymerization is inhibited by oxygen in the air. On the other hand, when the resin cement is cured only by photo polymerization, in cases where prosthetic materials of low light transmittance such as crowns are adhered or cavities occurred by caries are filled, it is difficult to cure resin cement sufficiently because parts where light can not reach exist.
Therefore, a dual-cure type resin cement becomes popular in which photo polymerization as well as chemical polymerization occurs in order to achieve sufficient polymerization even in parts where light cannot reach so as to use for prosthetic materials of low light transmittance while curing at a surface part is promoted by photopolymerization by light radiation.
Such a dual-cure type resin cement may contain a variety of polymerizable monomers and reactive components such as red-ox type polymerization initiators and the like.
For a conventional powder-liquid type of resin cement, there is no concern about reaction among a variety of components as far as they are packed prior to mixing. However, for a two-paste type composite resin cement, it is possible that a variety of components react in pastes to reduce storage stability of the pastes.
Accordingly, in a field of dental prosthetic and restoration, it is recently desired to invest the dual-cure two-paste type composite resin, which is excellent in mechanical strength and workability, with storage stability.
In order to improve adhesiveness of a composite resin cement to bio hard tissues such as tooth substances, primers pre-treating a tooth surface have been used prior to application of composite resin cement to the tooth substances.
Japanese Patent No. 2670522 [Patent Document 2] discloses in its specification a primer compound used for hard tissues such as tooth substances. This primer demineralizes a tooth to make a surface tooth rough by acid etching. An adhesion mechanism is supposed that resin cement penetrates into fine structures of the rough surface and the resin cement cures in this state to form mechanical connection between the resin cement and the tooth surface.
As described above, demineralization by acid etching damages tooth substances. Further, a dental hard tissue comprises enamel and dentin, and adhesiveness to both enamel and dentin is clinically required but it is not considered that an adhesion strength of a resin cement to a surface of hydrophilic dentin is sufficient.
Japanese Patent No. 2634276 [Patent Document 3] discloses in its specification a primer improving adhesiveness of a resin cement both to enamel and dentin without a treatment which will damages a tooth surface such as acid etching and the like.
This primer comprises a polymerizable compound containing acidic groups such as a carboxyl group and a phosphate group and the like.
Japanese Patent No. 2865794 [Patent Document 4] discloses in its specification an adhesive composition comprising: (a) a (meth)acrylic ester derivative containing a phosphonate group represented by the general formula (I):
wherein R1 is a hydrogen atom or a methyl group, R2 is an alkylene group having a carbon number of 5 to 10, R3 is an alkylene group having a carbon number of 1 to 6 as a polymerizable compound containing acidic groups; (b) at least one kind of radical polymerizable monomers; (c) at least one kind of polymerization initiators. When the phosphonate group contained in the (meth)acrylic acid ester derivative is applied on tooth substances, the phosphonate group chemically connects with calcium components in the tooth substances and, consequently polymerizable groups are attached on a surface of the tooth substances. By copolymerizing these polymerizable groups and other polymerizable monomers in the resin cement, adhesiveness of the resin cement to the tooth substances may be improved.
The adhesive composition includes a dental adhesive composition, a dental compound filler, a hard resin adhesive for crowns and the like. For example, a powder material such as silica and the like may be added to the above composition to manufacture an adhesive resin cement.
Japan Patent No. 3449755 [Patent Document 5] discloses in its specification a primer composition comprising: (a) a vinyl compound containing acidic groups such as a phosphonate group and the like as a polymerizable compound containing acidic groups; (b) a water soluble vinyl compound containing hydroxide groups; (c) water; (d) an aromatic sulfinic acid salt and (e) an aromatic secondary or tertiary amine. The primer compound is provided as an adhesive kit with a specific acrylic adhesive, wherein acrylic monomers are used as the specific acrylic adhesive.
According to the adhesive kit, a high adhesion strength is achieved to enamel and dentin of tooth. However, when a vinyl compound containing acidic groups is used in a resin cement, there is a problem that polymerization curing is suppressed and sufficiently cured material cannot be obtained.
JP 10-251115A [Patent Document 6] discloses in its specification a dental primer mainly comprising (A) a phosphate group-containing polymerizable monomer as a polymerizable monomer containing acidic groups; (B) a multi-valent carboxylate group-containing polymerizable monomer and (C) water.
According to the dental primer, adhesion strength of 20 MPa or higher may be achieved both to dentin and enamel.
JP 2000-204010A [Patent Document 7] discloses in the Specification a primer compound comprising (A) a sulfonate group-containing polymerizable monomer as a polymerizable compound containing acidic groups; (B) a water soluble polymerizable monomer and (C) water. The primer compound is provided as a dental adhesive kit with a specific adhesive, wherein acidic phosphoric acid ester multi-functional polymerizable monomers are used as the specific adhesive.
According to the dental adhesive kit, an adhesion strength of 20 MPa or higher may be achieved both to dentin and enamel.
However, with respect to any one of dental primer compositions disclosed in Patent Documents 4 to 7, it is not obvious whether sufficient adhesion strength can be achieved both to enamel and dentin when they are used in a two-paste type dual cure composite resin cement.
[Patent Document 1] Japanese Patent No. 1784478
[Patent Document 2] Japanese Patent No. 2670522
[Patent Document 3] Japanese Patent No. 2634276
[Patent Document 4] Japanese Patent No. 2865794
[Patent Document 5] Japan Patent No. 3449755
[Patent Document 6] JP 10-251115A
[Patent Document 7] JP 2000-204010A